Trash them. Even when polished they'll likely disintegrate - mine were crumbly as hell. I'd prefer something which might provide some protection!
Here's what I just came up with and am pleased with how it looks. I bought a set of
these from Grainger and some of
these brackets from McMaster, opened up the holes on the long side for a 1/4" bolt to pass through, and here's how it turned out. Not perfect but I think it looks fine and should hold up.
Plus, with the steel hardware, I can easily make new ones in the future by cutting some PC to a desired size and drilling a couple of holes.